Hydraulic servomotor and the like



May 20, 1952 R. WESTBURY x-:T AL

HYDRAULIC SERVOMOTOR AND THE LIKE 4 sheets-sheet 1.

Filed May 27, 1950 May 20, 1952 R. wEsTBuRY ET AL 2,597,419

HYDRAULIC SERVOMOTOR AND THE LIKE Filed May 27, 1950 4 Sheets-Sheet 2 gf MW 1: @www May 20, 1952 R. WESTBURY ETAL 2,597,419

HYDRAULIC SERVOMOTOR AND THE LIKE Filed May 27, 195o I 4 sheets-sheet s May 20, 1952 R. WESTBURY ETAL 2,597,419

HYDRAULIC sERvoMoToR AND THE LIKE Filed May 27, 195o 4 'sheets-sheet 4 Patented May 20, 1 952 2,597,419 v HYDRAULIC SERVOMOTOR AND THE LIKE Roy Westbury, Bridgnorth, and Stanley Ralph Tyler, Willenhall, England, assignors .to H. M. Hobson Limited,l London, England, a company of Great Britain 'Appiieafion'fMay 27, 1950, serial No. 164,655

In Great Britain June 2, 1949 This invention relates to systems for the hy-I draulic control of an output member of the kind comprising a hydraulic actuator (i. e. a jack or motor) controlled by a control valve; operable by a manually operated input member to establish alternative pressure and exhaust connections to the actuator to cause vthe output" member to move in a direction and to an extent determined by the movement imparted to the input member.

As a safety measure against rfailure of the pressure Supply, or leakage in the system, it would be possible to duplicate the system and to provide two actuators in tandemor in parallel, both operating on the output member and each .having a separate control valve' and deriving pressure liquid from a separate pressure supply, the two control valves being operated by a common input member. Mere duplication, however, does not guard against the results arising from seizure oi one of the control valves. -This may cause disastrous results. in the case of operation of control surfaces of aircraft, as the valve seizes in an open position the pressure liquid may drive the control surface to an undesired extreme position. V

With a view to avoiding this disadvantage, the invention provides a hydraulic system of the above kind comprising a collapsible `member linked to the input member and adapted to'collapse when subjected to a predetermined load as the result of valve seizure and consequent excessive application ofv ,manual force tothe input member, and a valve, arranged to be opere ated by collapse of the collapsible memberito short circuit the actuator by establishingidirect liquid communication between thereof,

Consequently, if the control valve seizes and the collapsible member is collapsed by reason of opposite.V sides the application of increased force to the input member, the output member may be operated by another actuator deriving pressure from an alternative supply.

Preferably the valve actuated by collapse of the collapsible member is also arranged to cut off the pressure supply to the control valve.

Two embodiments oi the invention will now be described in detail, by way of example, with reference to the `accompanying drawings, in which:

c'claims.- (creo-97) 'i Figs. 3 and 3a are diagrams showing the alO- plication of the invention to a system embodying two hydraulic motors.

. VLilre reference numerals indicate like parts throughout the figures.

4Considering Fig. l, first of all, the installation shown therein includes a hydraulic jack I0, the

Fig, 1 is a dierammatic showing of a hydraulic jack according te the invention,

Fig. 2 is a diagram showing the application of the invention to a system ,embodyingtwo hydraulic jacks in tandem, and

piston II of which carries a piston rod I2, which projectsfrom the jack cylinder I3; and is provided at I4 to a fixed point I5 of the aircraft structure. Inside the piston rod is a pressurising piston I6 loaded by a spring Il, the piston i6 serving to apply pressure, through a hole IB in thepiston rod I2, to the liquid contained in the cylinder i3.

The cylinder I3 is pivoted, at I9, to an output member y2li for applying movement, as the cylinderl I3moves in relation to the jack piston II. to an aileron or other control surface 2|. The object of the pressurisihg piston I3 is to maintain maximum rigidity of the liquid in the connection between the control surface 2| and the aircraft, for the purpose of preventing flutter of the control surface.

Fixed to the cylinder I3 are:

(a) The housing 22 of a collapsible member 23 (b) A pair of stops 24,

(c) A control valve housing 25,

'(d) The housing 26 of a pair of non-return valves,

`(e) The housing 2l of a supply check valve and a jack by-pass valve, and (f) Thehousing 28 of a return check valve. ,-Fig. 1 being purely diagrammatic, the connections Ibetween the cylinder I3 and the parts. 22 and 24--28 are not shown therein.

An input member 29, connected to the pilots control column, carries a projection 30 which moves with clearance between the stops 24 during normal operation of the jack. The input member 29 is pivoted at 3l to a link 32 pivoted at one end, 33, to the collapsible member 23 and at the other end, 34, to a link 35 for imparting movement to the control valve 33 of the jack.

Liquid under pressure, supplied through an inlet 31, normally holds a tubular non-return valve 38 open, against a spring 39, and so obtains access to a line 40 controlled by the middle land of the control valve 33. The hydraulic pressure also urges to the right, against a spring 42, a piston d3, thereby holding a non-return valve 44 open against its spring 45. This places in communication with au exhaust outlet 46 lines-4l controlled by the outer lands of the control valve 33.

i 'D11-fille llrml Operation of the jack, the link 3 32 will. on movement of the input member 29. pivot about the point 33 and displace the control valve 36 to connect, in conventional fashion, through lines 48, 49 one end of the cylinder I3 to pressure and the other to exhaust. The cylinder I3 will then move, in the same direction as the control valve 36, until the housing 25, which travels with it, causes the lands of the control valve again to mask the ports in the housing communicating with the lines 40, 41. 'I'he cylinder I3 thus moves to an extent and in a direction determined by the movement of the input member 29.

In the event of failure of the hydraulic pressure. the non-return valves 38, 44 close to trap liquid in the jack. Manual operation of the jack is then possible by moving the input member 29 suilciently for it to actuate one or other of the stops 24 to move the jack cylinder I3. When the input member 29 is so moved, the central land of the control valve 36 opens a port 50 to allow, as described in U. S. application 785,837, now Patent No. 2,566,273, dated August 28, 1951, trapped liquid to circulate from one end of the cylinder to the other through one or other of a pair of non-return valves I I The collapsible member 23, which is described in detail in U. S. application Serial No. 164,653 serves to deal with the contingency of the control valve 36 seizing in its housing 25 during normal hydraulic operation of the jack. It comprises a cylindrical tube 5I, which is a close fit in a cavity in the housing 22 and free to slide therein, a plunger 52 slidable in the tube 5I, a plurality of balls 53, and a compression spring 54. The tube 5I is pivoted at 33 to the link 32 and the spring 54 is mounted in compression between the head of the plunger 52 and the end of the tube 5I. The balls 53 project through holes 55 in the tube 5I and into holes 56 in the housing 22 and normally the outer and smaller portion of each ball 53 projects into and fits closely within the holes, 55, 56. The plunger 52 has an inwardly tapering head 51 which presses the balls 53 outwards into the position illustrated.

'I'he balls 53 consequently resist sliding movement of the tube 5I in relation to the housing 22, as such movement would necessitate that the balls ride inwardly down the tapered face of the head 51 and consequently in movement of the plunger 52 to the right, thereby increasing the compression of the spring 54. When, however, the load seeking to move the tube 5I axially in relation to the housing 22, and imposed thereon by the pilot in the effort to free the control valve 36, when seized, reaches a predetermined limit, the balls 53 will be moved inwardly to an extent suicient for them to cease resisting movement of the tube 5I, with the result that the member 23 is collapsed.

A resetting plug 58, having a conical head 59, may be moved into the tube 5I, to reset the member 23. After the tube 5I has been moved back into position to align the holes with of the cylinder I3, while the other end of the cylinder communicates with a port 61 in the annular chamber 66 which is normally sealed by the end of the spring-loaded plunger 60. Thearea of the port 61 is equal to half the cross-sectional area. of the portion of the plunger steml enclosed in the annular chamber 66, so that the plunger is subjected to equal upward loads by a givenpressure existing in either end of the cylinder.

A subsidiary function of the spring-loaded plunger 60 is to prevent excessive pressure being generated at either end of the cylinder I3 due to excessive reaction load from the control surface 2l. The leaf spring 6I is so designed that the plunger 6|), may lift against it, under excessive pressure on its lower end, or on the differential area thereof exposed to the pressure in the chamber 66, thereby relieving the pressure in the cylinder. The' plunger 60 will of course move down again togsealing position when the reaction load has returned to a safe value.

The main function of the spring-loaded plunger is however fulfilled when the collapsible member 23 collapses due to seizure of the control valve 36. The catch 65 is then removed from the catch.64 on the leaf spring 6I, which is thus disabled. .whereupon the plunger 60 is lifted by the hydraulic pressure acting on its lower end, affording. free communication between the two ends of the cylinder I3. As the plunger 6U lifts, a collar 66 on it closes the non-return valve 38 and cuts off the pressure supply to the control valve 36. l

As communication is opened between the two ends of 'the cylinder I3 when the collapsible member 23 collapses. the system oifers no resistance to movement of the control surface 2l by a second hydraulic system, which may be constituted by an exactly similar hydraulic jack, deriving pressure from a different source, and the control valve of which is also linked to the pilots input member 29.

In the-case of the installation shown in Fig. 2, two jack pistons II, Ila are mounted in tandem on a common piston rod I2, pivoted at I4 to the aircraft structure and movable respectively in cylinders I3, I3a in a common housing I I3 which constitutes an output member connected to a contrlsurface or to the head of the rotor of a helicopter. Movement of the housing II3 thus servesto impart-movement to the control surface to adjust the rotor head, e. g. by varying the blade pitch or by tilting the rotor head.

Parts" associated with the jack piston II bear the .same reference as the corresponding parts in Fig. l, while parts associated with the jack pistonV IIa bear the same reference numerals as the corresponding parts associated with the jack piston II, but with the addition of the suilix a;

The pilots input member 29 is connected to a member 69, pivoted at 10 and having a nose 1I which is movable between the stops 24. The member 69 is connected, by links 12, 12a to links 32, 32a.

Normally, movement of the input member 29 will-rock the links 32, 32a in opposite directions about their points 33, 33a of pivotal attachment to their respective collapsible members 23, 23a to move the control valves 36, 36a in the same direction, thereby admitting hydraulic iiuid to the corresponding ends of the two cylinders I3, I3aand establishing exhaust connections to the opposite ends of the jack cylinders.

If. however, oneofltheco'ntrol valves, say the Vcontrol valve 36, seizes, the :force exerted by a pilot 'on .the `input Vmember 29 will collapse the associated vcollapsible member 23. The associated valve v6,9 will then move, precisely as described with reference to Fig. 1, to cut off the pressure supply from the associated control valve 36 and to establish a `by-pass connection between oppositeends'of thejack cylinder |3. The failed `jack then offers `no resistance to continued` operation of the output member by the other jack. which is control-led by its control valve 36a. After the member 2-3 has collapsed, the link 32 turns idlyJ in response to movement of the input member, 29, about its point of attachment 34 to the seized control valve 38. Stops (not shown) serve `to limit the lmovement yof the valve 36.

In the arrangement shown in Figs. 3 `and 3a, two hydraulic motors 83, 83a serve to operate a control surface. Parts associated with these motors which correspond to parts shown in Fig. l bear the vsame reference numerals. Also parts associated with the motor 83a which correspond to parts associated `with the motor 83 bear the :same reference numerals, with the addition of the'suiiix a.

The vpilots input member 29 is connected vtb a link 84 which, on movement of the input member, turns .about a pivot 85 to shift a linkage '83, 8l, 81a, |87, |8111, thereby moving the two control valves 36, 36a in the same direction.

But one of the hydraulic motors, 83, will be described, lthe -other 83a, being of precisely similar construction. The motor 83 comprises a .shaft 88, carrying a pair of eccentrics 89, 99 spaced at 180 (i. e. in antiphase) on the shaft. Associated with the eccentric B9 is a set of six cylinders, each containing a piston 9|, these cylinders being located radially in relation to the shaft 88. A similar set of six cylinders each containing a piston 92, is associated with the eccentric 98. Associated with each aligned pair of cylinders is one of six distributing valves 93, each of which is held by a spring 94 in contact with a swashplate 95 on the shaft 88. For `simplicity but :one pair of aligned cylinders, containing vpistons 9|, 92, and but one associated distributing valve 93, are shown in Fig. 3a. The motor has a drain connection |93 for leading away liquid which may leak past the pistons 9| 92 .or the distributing valves 93.

On displacement of the control valve 39, it establishes alternative pressure and exhaust connections to lines 96, 97 leading to each of the distributing valves 93.. This results in sympathetic movement of the pistons 9|, 92 thereby actuating the eccentrics 89, 99 to rotate the shaft 88 in a direction determined by the direction of movement of the control valve 36. Thus, if line 95 is connected to pressure, and line 91 to exhaust, the piston 92 will be caused to move in and the piston 9| to move out. As the shaft 88 rotates, the swash plate 95 imparts continuous reciprocating movement to all of the valves 93 so that the associated pistons 9|, 92 will be alternately connected, at the proper times, to pressure and exhaust.

The shafts 88, 88a of the two motors drive, through gear wheels 98, 98a a common gear wheel 99 connected, by bevel gearing |99, to a threaded sleeve |0|, engaging a pair of screw jacks |02 which are moved inwards or outwards, according to the direction of rotation of the member Illl, to impart movement to the two portions of the control surface, not shown.

In screw threaded engagement with the boss of the gear wheel `99 isa follow-up rod.|03 which operates, by rocking the `link 84 about its pivotal attachment |99 to the 'input member 29, to'returnthe control valves 36, 391Mo neutral position.

If either of the control valves, say 36, should seize, the following sequence of events occurs. The ,associated collapsible member 23 collapses, thereby freeing the catch 1l associated with the corresponding valve |69, which lcloses under the action lof its spring '18. This vcuts off pressure Vfrom the control valve 35., and also from a line |05. As long as `there is pressure in the line |95, a vplunger is held, against the action of a spring |91, to maintain contacts |98., |99 closed. When the pressure is `cut orf, the spring |07 causes .the contacts |08, |99 .to be separated, :thereby lighting a warning lamp. When the valve k| closes, `its stem :II-'moves into position to open 'a connection vbetween the lines 96, .97, thereby allowing the hydraulic motor 83 to run freely, as it is driven `through the gears 99, 98, Yon ycontinued .operation of the Ystill effective motor 93a.

Onseizure of the control valve 39a, a lprecisely similar action takes Jplace. -The member 23a collapses and the valve |60a closes, to cut on pressure from the valve 36a, 'to energize the associated warning lamp, vand to connect together the lines Interlocking plungers 1H, |||a are provided between extensions |2, |2a of the tubes 5|, 51a 'of the two collapsible members 23, 23a. These operate, as described in U.v S. application lSerial No. 164,759 when veither of the members 23, 23a collapses, to lock the other against collapse.

The invention, in its application to duplicated hydraulic actuators, is of utility only when applied to .actuators directly coupled to the output member, e. g. jacks in tandem, as shown in Fig. 2, jacks -in :parallel and both directly coupled tc the output memberandmotors mounted in tandem on or directly geared to a common output shaft. In the case of `actuators differentially coupled to the output member, i. e. jacks in parallel coupled tothe output'member through a differential link as described in U. S. application Serial No. 164,654,01' motors coupled to the output rmember through a differential gearing, a failed and short-circuited actuator can be driven in reverse by the still operative actuator, and it is necessary to provide a pressure responsive lock which operates in case of failure, e. g. as described in U. S. application Serial No. 164,654, to lock `the failed actuator.

What we Vclaim as our invention land desire to secure by Letters Patent is:

'1. The combination with a hydraulic actuator having aninlet for liquid under pressure and an exhaust outlet. of a manually operable input member and an output member adapted to be actuated by the actuator, said actuator comprising a control valve movable in opposite directions'by said 'input member to cause liquid to now 'through said actuator' in alternative paths from said inlet to said outlet and thereby to cause said actuator to move said output member in a direction and to an extent determined by the movement imparted to said input member, a collapsible member linked to the input member and arranged to collapse, in the event of seizure of said control valve and consequent abnormal application of manual force to said input member, a conduit for permitting of free circulation of liquid within the actuator, a valve normally closing said conduit, and means controlled by the collapsible member and operative on collapse thereof to cause automatic opening of said valve.

2. 'I'he combination with a hydraulic actuator having an inlet for liquid under pressure and an exhaust outlet, of a manually operable input member and an output member adapted to be actuated by the actuator, said actuator comprising a control valve movable in opposite directions by said input member to cause liquid to flow through said actuator in alternative paths from said inlet to said outlet and thereby to cause said actuator to move said output member in a direction and to an extent determined by the movement imparted to said input member, a collapsible member linked to the input member and arranged to collapse, in the event of seizure of said control valve and consequent abnormal application of manual force to said input member, a conduit for permitting of free circulation of liquid within the actuator, a valve subject to hydraulic pressure within the actuator, and a catch controlled by the actuator for normally holding said valve closed, said catch being disabled on collapse of the collapsible member to permit said hydraulic pressure to move said valve to open said conduit.

3. The combination with a hydraulic actuator having an inlet for liquid under pressure and an exhaust outlet, of a manually operable input member and an output member adapted to be actuated by the actuator, saidv actuator comprising a control valve movable in opposite directions by said input member to cause liquid to ow through said actuator in alternative paths from said inlet to said outlet and thereby to cause said actuator to move said output member in a direction and to an extent determined by the movement imparted to said input member, a collapsible member linked to the input member and arranged to collapse, in the event of seizure of said control valve and consequent abnormal application ofmanual force to said input member, a conduit for permitting of free circulation of liquid within the actuator, a valve for closing said conduit, a catch controlled by the collapsible member for normally maintaining the valve in closed position, and a spring urging the valve to position to open said conduit, said catch being disabled, on collapse of said collapsible member, to permit said spring to open said valve. A

4. In combination, a pair of hydraulic actuators each having a pressure inlet and an exhaust outlet, an input member common to the two actuators, and a common output member adapted to be actuated by the two actuators, each actuator comprising a control valve movable in opposite directions by said input member to cause liquid to ow through said actuator in alternative paths from said inlet to said outlet and thereby to cause said actuator to move said output member in a direction and to an extent determined by the movement imparted to said input member, a collapsible member linked to the input member and arranged to collapse, in the event of seizure of said control valve and consequent abnormal application of manual force to said input member, a conduit for permitting of free circulation of liquid within the actuator, a valve normally closing said conduit, and means controlled by the collapsible member and operative on collapse thereof to cause automatic opening of said valve, said actuators being directly coupled to said output member.

5. The combination with a hydraulic jack, comprising a servo member and a housing therefor, of a manually operable input member, an output member coupled to the jack, a pressure inlet, an exhaust outlet, a control valve coupled to the input member and movable in opposite directions from a neutral position to establish alternative connections between opposite ends of said housing and said inlet and outlet and thereby cause relative movement between said housing and servo member to move the output member in a direction and to an extent determined by the movement imparted to the input member, a collapsible member coupled to the input member and arranged to collapse, on seizure of said control valve, under application of manual force to the input member, a conduit for permitting liquid to iiow freely between opposite ends of said housing, a normally closed valve in said conduit, and means controlled by said collapsible member for freeing said valve, on collapse of said collapsible member, for automatic movement to its open position.

6. The combination with a hydraulic motor, of a manually operable input member, an output member actuable by the motor, a pressure inlet, an exhaust outlet, a control valve movable by said input member in opposite directions from a neutral position to establish a ow of liquid through said motor from said inlet to said outlet in alternative directions according to the direction of movement of said control valve and thereby to cause said motor to move said output member in a direction and to an extent determined by the movement imparted to the input member, a collapsible member coupled to the input member and arranged to collapse, on seizure of said control valve, under application of manual force to the input member, a conduit for permitting liquid to circulate freely through said motor, a normally closed valve in said conduit, and means controlled by said collapsible member for freeing said valve, on collapse of said collapsible member, for automatic movement to its open position.

ROY WESTBURY. STANLEY RALPH TYLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,315,110 Dornier Mar. 30, 1943 FOREIGN PATENTS Number Country Date 582,380 Great Britain Nov. 13, 1946 

